Distillation of metals



Nov. 30, 1965 1-. R. A. DAVEY ETAL 3,220,827

DISTILLATION OF METALS Filed Feb. 1, 1963 3 et -Sheet 1 735 1 amz zmi m 1955 T. R. A. DAVEY ETAL 3,220,327

DISTILLATION OF METALS 3 SheetsSheet 2 Filed Feb. 1, 1963 T. R. A. DAVEY ETAL 3,220,827

DISTILLATION OF METALS Nov. 30, 1965 3 Sheets-Sheet 5 Filed Feb. 1, 1963 141m flak/Wi w,mmy hxm United States Patent 3,220,827 DHSTHLLATIGN GF METALS Thomas Ronald Albert Davey and Stephen Esslemont Woods, Avonmouth, England, assignors to Metallurgical Processes Limited, Nassau, Bahamas, a corporation of the Bahamas, and The National Smelting Company Limited, London, England, a British company Filed Feb. 1, 1953, Ser. No. 255,543 Claims priority, application Great Britain, Feb. 21, 1962, 6,683/62 18 Claims. (Cl. 75-63) This invention relates to evaporation and distillation from a falling film of liquid. The invention particularly relates to the provision of a splash-free film in such distillation.

In one application of the present invention zinc is separated from zinc-containing lead under vacuum in a substantially circular vessel in which zinc-containing lead is caused to flow in a thin, even film over the downward and inward sloping side of a frusto-conical spreading means which is concentrically arranged within the vessel so that zinc is evaporated from the lead and condensed on a cooled surface at the centre of the vessel.

To ensure even flow of the said lead, the lead may be run into a relatively small annular launder or trough surrounding the top of the spreading tube which is maintained level so that the lead overflows evenly and forms a thin uniform film over the spreading tube. This top may be formed with a weir profile as described more fully below.

This method of maintaining an even flow of lead has been found etficient for moderately small flow rates of lead in such a vessel. However, when the rate of lead flow through the vessel was greatly increased, unexpected splashing of the lead occurred from the weir and spreading tube. This splashing caused droplets of lead to be carried over to the cooled surface with the zinc vapour, thus causing an intolerably high lead content in the zinc recovered. It has been found impossible to eliminate this splashing merely by adjustments of level to either the launder or the weir.

It is an object of the present invention to overcome this tendency to splash and to facilitate the evaporation of a volatile constituent from the descending liquid.

The invention consists in a method of ensuring even distribution of and facilitating evaporation of a volatile constituent from, liquid flowing in a thin film over an inclined spreading means in which movement of the liquid is so controlled that it flows over the top of the spreading means with a transverse component to its motion.

The invention further consists in a method of separating zinc from zinc-containing lead by passing the molten zinc-containing lead under vacuum down the inner inwardly tapering surface of a frusto-conical spreading tube in a thin film and collecting the zinc distilled off, in which the movement of the zinc-containing lead is so controlled that it flows over the top of the frusto-conical spreading tube with a transverse, i.e. tangential component to its motion.

The tangential component of the motion may be imparted to the liquid either as, or before, it flows over the top of the spreading means.

The invention further consists in apparatus for extracting a volatile constituent from a liquid mixture comprising a vacuum vessel containing a hollow tapering spreading means with its broad end uppermost and surrounded by a space capable of holding the liquid mixture at the level of the top of the spreading means so that in operation the liquid mixture flows over the inside surface of the hollow tapering means, and means for ensuring that the liquid flow has a tangential component.

In such an apparatus used for separating zinc from Zinc-containing lead, these means may be a lead supply pipe which enters the lead holding space at such an angle as to impart a circulatory motion to the zinc-com taining lead in the space when the apparatus is in use.

It is preferred to form the apparatus for separating zinc from zinc-containing lead as a substantially circular vacuum vessel within which is concentrically positioned a frusto-conical spreading tube surrounded by two intercommunicating concentric launders, from the inner of which zinc-containing lead flows down the inner surface of the frusto-conical spreading tube.

In such an apparatus, a tangential flow motion may be brought about by deflecting vanes around the top of the spreading tube which are positioned at an angle to the radii of the tube.

If the alternative method, in which the tangential motion is imparted before the zinc-containing lead flows over the top of the spreading means, e.g. a weir at the top of the tube, is used, the apparatus may comprise means for directing the zinc-containing lead from the outer to the inner launder so that it enters the launder at an angle to a radius and a circulatory motion is set up in the inner launder. This may be effected by tubes (so formed as not to project within the inner launder and impede the circulatory motion set up) in a dividing wall of the inner and outer launders at a low angle to the wall or alternatively by forming the wall as a series of angled plates and thus defining between adjacent plates 21 series of spaces each at an angle to a radius passing through it.

In a modification, the inner launder may be dispensed with and the outer launder be provided with a supply tube for zinc-containing lead at, or at a small angle to, a tangent to the launder.

The apparatus described in the four preceding paragraphs may also have a portion of the frusto-conical tube near the top profiled so as to give a Weir of appropriate shape to minimise or eliminate splashing.

In the method according to the invention as applied to the separation of zinc, and using the apparatus as described in any of the five preceding paragraphs, the velocity of circulation of zinc-containing lead depends upon the difference in zinc-containing lead level in the two launders (or, in the single-launder modification, upon the speed of Zinc-containing lead supply). This in turn depends upon the head over which the vacuum in the vessel has to draw the Zinc-containing lead, and may also be varied, e.g. by supplying the Zinc-containing lead under pressure.

The invention will be further described with reference to the accompanying drawings which illustrate the invention as applied to a vacuum process for the removal of Zinc from lead, and in which:

FIGURE 1 is a vertical section through part of the apparatus.

FIGURE 2 is a section taken through II in FIGURE 1.

FIGURE 3 is a section taken in the same plane as FIGURE 2 of a different embodiment for imparting tangential flow.

FIGURE 4 is a similar section showing a third embodiment.

FIGURE 5 is a section taken through II--II of FIG- URE 4.

FIGURE 6 is a similar section to FIGURES 2, 3 and 4 of a fourth embodiment, and

FIGURE 7 is a section taken through line III of FIG- URE 6.

In FIGURE 1 a substantially circular vessel 1 is supported on surrounding wall 1a. Within and concentric with this vessel are cooling coils 2, frusto-conical spreading tube 3, having an upper portion 3a and a top 3b, inner launder- 4 and outer launder 5, the launder 5 being an annular chamber defined between the tube 3 and the wall of the vessel, and launder 4 being defined by the upper portion 3a of tube 3 and a surrounding angled metal sheet 6. Outer launder 5 connects via angled barometric inlet tube 7 with lead-holding bath 8 (it will be appreciated that since the vessel 1 is under vacuum, lead will rise in tube 7 and pass into launder 5) In operation, lead runs uniformly over the circular top 3b of tube 3 and falls in a thin film down the tube, in the process losing the zinc vapour which accumulates as zinc metal upon the cooling coils 2. Such an accumulation is shown at 9.

We have found that the lead passing over the top 3b shows substantially less tendency to splash over with turbulent fiow and contaminate the accretion of zinc 9 if a tangential component of velocity is present and that accordingly higher throughputs of zinc-container lead may be allowed.

The centrifugal force exerted by the swirling motion at 3b holds the lead film on to the weir and spreading surface, preventing the film from leaping out and splashing. The profile of the weir is chosen so as to give a smooth flow of lead from its horizontal flow over the weir lip to its almost vertical flow down the spreading tube.

Various methods may be used to impart a tangential velocity to the molten lead. One way of ensuring this is shown in FIGURE 1, in which 11 shows one of a series of tubes interconnecting the launders 4 and 5. These tubes pass through the sheet 6 at an angle, as is more clearly shown in FIGURE 2.

On FIGURE 1 the lead in outer launder 5 is at a level 5a higher than that of the top 3b of tube 3. Thus, as lead runs over the top of the tube 3b more lead passes into the launder 4 via tubes 11. This lead passes into the inner launder at an angle, and the whole of the lead in the inner launder in fact circulates around the inner launder because of this. It therefore runs over the top 3b of tube 3 with a tangential component of motion and runs down tube 3 as shown by the arrows in FIGURE 1. It will be observed that tubes 11 do not project into the inner launder 4. This gives a streamlined flow at the dividing wall 6.

More especially for low flow rates of lead, the arrangement of FIGURE 3 may be adopted. In this, inner launder 4 is not used, but the remaining launder 5 is fed tangentially (via barometric inlet tube 7) from a holding bath such as shown at 8 in FIGURE 1.

With high flow rates in an arrangement of this type, there may be a tendency for the liquid to flow rather unevenly over the part of the tube 3 nearest the lead inlet; thus at high flow rates some other embodiment using an inner launder would be beneficial.

In FIGURES 4 and 5, a further method of ensuring tangential flow is shown. In this embodiment an inner launder 4 is used fed from outer launder 5 by virtue of its higher lead level 5a. In this case, however, lead passes from 5 to 4 via holes 12 which do not impart a tangential motion; the tangential motion is imparted to the lead as it flows over the top 3b of the tube 3 by the deflecting vanes 13 which are welded to the top 3b of tube 3 at an angle with respect to a radius.

In a further modification of the embodiment of FIG- URES 4 and 5, FIGURES 6 and 7 show an arrangement in which the whole wall of the inner launder 4 is composed of angled plates 14 welded to the launder bottom 15. As will be evident from FIGURES 6 and 7, these plates have the same function as tubes 11 of FIGURES 1 and 2, since they impart a tangential motion to the lead before it passes over the top of tube 3.

The lead depleted of zinc (FIG. 1) passes out by outlet 10.

The slope of tube 3 in the foregoing embodiments is conveniently about 10 in 1. Any slope much gentler than this results in the evacuated vessel 1 being less compact and therefore less able to stand the strain of evacuation.

By way of example, in the embodiment shown in FIG- URE 1, a suitable circumferential velocity for the liquid in the inner launder has been determined for lead as being a little less than one third of the circumference of the upper part of the tube per second. Thus in a vessel with a tube of six feet maximum diameter, a circumferential velocity for the lead of about 4 ft./sec. is satisfactory. Because of frictional losses, this will require an inlet velocity of about 8 ft./sec. which can be supplied by a 12" potential head drop between the outer and inner launders.

Similar results will obtain for the other embodiments.

Greater angular velocities can of course be produced by providing a greater potential head drop and this, by appropriate arrangement of levels of the holding bath 8 and the vessel, may be even greater than one barometric head of the liquid in question, while using only atmospheric pressure to force liquid through an evacuated vessel, or may, of course, be produced by a pump supplying liquid to the vessel.

Various modifications may be made within the scope of the invention.

We claim:

1. In the method of separating and recovering a relatively volatile constituent from a liquid complex containing the same in association with a less volatile constituent, the liquid complex being under vacuum in an enclosed space while it descends by gravity continuously as a film supported by the inner surface of an inverted generally circular hollow frusto-conical evaporating zone within the enclosed space, the larger end of the circular frustoconical evaporating zone being uppermost and the smaller end of the circular frusto-eonical evaporating zone being lowermost, maintaining within the frustoconical zone, and substantially in lateral opposition to the evaporating zone, a substantially concentric upright circular condensing zone for the more volatile constituent, maintaining the enclosed space under sutficient vacuum to evaporate progressively the more volatile constituent from the supported thin film of liquid complex, condensing the resulting vapours of the more volatile constituent in the upright condensing zone first as a solid cake and later as a liquid, progressively withdrawing from the enclosed space the condensed liquid of the more volatile constituent, and progressively withdrawing from the enclosed space the less volatile constituent while still in liquid form, the improvement which comprises the combination therewith of the steps of (a) flowing the liquid complex under pressure onto the inner and upper part of the hollow inverted frustoconical evaporating zone at a carefully controlled angular velocity;

(b) imparting a transverse tangential circumferential flow of the liquid complex around and in sweeping contact with the inner supporting distributing surface of the inverted frusto-conical evaporating zone;

(0) spreading the flowing liquid complex substantially evenly over the upper part of the inner supporting distributing surface of the inverted frusto-conical evaporating zone to form thereon a thin even film of the liquid complex;

(d) maintaining the transverse tangential flow of the thin even film of liquid complex in hugging contact with the inner surface of the inverted frusto-conical evaporating zone as the film of liquid descends in the evaporating zone;

(e) continuing the resulting swirling spiral flow of the thin even film of liquid complex on the supporting surface of the evaporating zone while vapourizing the more volatile constituent therefrom and condensing the resulting vapours on the cooler and condensed solid cake of more volatile constituent;

(f) allowing the even thin film of liquid to descend to the bottom of the inverted hollow frusto-conical evaporating zone and of the enclosed space without splashing to avoid contamination of the vapour from, and condensed solid cake of, the more volatile constituent with droplets of liquid containing the less volatile constituents;

(g) passing the thin even film of liquid from top to bottom of the evaporating zone without substantial volatilization of the less volatile constituent of the liquid; and

(h) removing separately the resulting liquids from the bottom of the inverted hollow frusto-conical evaporating zone and of the enclosed space.

thus effecting a relatively sharp separation and recovery of the more volatile constituent from the less volatile constituent of the original liquid complex.

2. Method according to claim 1, in which a continuously replenished annular stream of the liquid complex is circulated at carefully controlled velocity and pressure around the exterior upper portion of the inverted frustoconical evaporating zone, and the circulating annular stream of liquid complex is flowed continuously over the top of the inverted frusto-conical evaporating zone into the evaporating zone itself at a carefully controlled angular velocity to impart the desired tangential circumferential flow of the liquid complex into and around the frusto-conical evaporating zone.

3. Method according to claim 1, in which a plurality of circumferentially spaced streamlets of the liquid complex is fed under pressure continuously and tangentially into an annular stream of the liquid complex, the annular stream of liquid complex is circulated at controlled velocity and pressure around the exterior upper portion of the inverted frusto-conical evaporating zone, and th circulating annular stream of liquid complex is flowed continuously over the top of the inverted frusto-conical evaporating zone into the evaporating zone itself at a carefully controlled angular velocity to impart the desired tangential circumferential flow of the liquid complex in and around the frusto-conical evaporating zone.

4. Method according to claim 1, in which a plurality of circumferentially spaced streamlets of the liquid complex is fed under pressure continuously into an annular main body of the liquid-complex surrounding the exterior upper portion of the frusto-conical evaporating zone, and the annular main body of liquid-complex is flowed continuously over the top of the frusto-conical evaporating zone into the trusto-conical evaporating zone itself at a carefully controlled angular velocity to impart the desired tangential circumferential flow of the liquid-complex around the frusto-conical evaporating zone.

5. Method according to claim 1, in which a contained continuously replenished inner annular 'body of the liquid complex is formed around the exterior upper portion of the frusto-conical evaporating zone, a separately contained continuously replenished outer annular body of the liquid complex is formed around the exterior of the inner annular body of liquid complex, liquid complex is continuously passed from the outer annular body to the inner annular body, maintaining the level of the outer annular body of liquid complex at a substantially higher level than the top of the frusto-conical evaporating zone and the normal liquid level in the inner annular body to establish a hydro-static head in the outer annular body for accelerating the flow of liquid complex from the outer annular body to the inner annular body, and liquid complex in the inner annular body is flowed continuously under pressure into the evaporating zone at a controlled angular velocity.

6. Method according to claim 1, in which the liquid complex is molten zinc-containing lead, and the zinc is the more volatile constituent and the lead is the less vola tile constituent.

7. Method according to claim 2, in which the continu ously replenished annular stream of liquid complex is molten zinc-containing lead, and the zinc is the more volatile constitutent and the lead is the less volatile constituent.

8. Method according to claim 3, in which the circumferentially spaced streamlets and the annular stream of liquid complex are formed of molten zinc-containing lead, and the zinc is the more volatile constituent and the lead is the less volatile constituent.

9. Method according to claim 4, in which the circumferentially spaced streamlets and annular main body of liquid-complex are formed of molten zinc-containing lead, and the zinc is the more volatile constituent and the lead is the less volatile constituent.

10. Method according to claim 5, in which the liquid complex in the outer and inner annular bodies is molten zinc-containing lead, and the zinc is the more volatile constituent and the lead is the less volatile constituent.

11. In apparatus for separating and recovering a relatively volatile constituent from a liquid complex containing the same in association with a less volatile constituent, such as molten zinc-containing lead, the zinc being the more volatile constituent and the lead being the less volatile constituent, including a generally circular vacuum chamber, a substantially vertical hollow inverted generally circular frusto-conical distributing tube disposed within and spaced from the side wall of the chamber, the larger end of the frusto-conical tube being uppermost and the smaller end being lowermost, an annular launder for the passage of the liquid complex located between the side wall of the chamber and the exterior of the frusto-conical tube, means for feeding liquid complex continuously into the launder, an upright condenser for the more volatile constituent disposed concentrically in the center portion of the chamber spaced a suitable distanoe from the frusto-conical tube, said condenser being adapted to support on its outer peripheral surface a relatively thick solid cake composed of said more volatile constituent to provide a condensing surface for more vapours of the more volatile constituent in liquid form, means for progressively discharging from the chamber liquid rich in said more volatile constituent, and means for progressively discharging from the chamber liquid rich in said less volatile constituent, the improvement which comprises the combination therewith of devices associated with the annular launder for discharging liquid complex continuously fed therein into the frustoconical tube and onto its inner distributing surface with a tangential component to its motion of travel to produce a swirling spiral flow of thin even film of the liquid complex on the distributing surface.

12. Apparatus according to claim 11, in which the associated devices include means for circulating the liquid complex in the annular launder at a controlled circumferential velocity.

13. Apparatus according to claim 11, in which the associated devices include a barometric inlet tube connecting the annular launder at an acute angle with a source of liquid complex so that the liquid complex may enter the launder tangentially to circulate the liquid in the launder.

14. Apparatus according to claim 11, in which the associated devices include an outer wall surrounding the launder, the wall extending substantially higher than the top of the frusto-conical tube to inhibit outward splashing of the liquid complex from the launder.

15. Apparatus according to claim 11, in which the annular launder constitutes an inner laundry immediately adjacent the periphery of the top portion of the frustoconical tube and an outer annular launder surrounding the inner annular launder, the associated devices include a plurality of circumferentially spaced upright plates set at an acute angle to the outer periphery of the frustoconical tube and integrally secured to the bottom of the inner launder to separate the two launders in a sub-divided manner, the plates extend upwardly from the bottom of the inner launder substantially above the level of liquid complex normally confined in the two launders, each plate extends part Way into the outer launder and part way into the inner launder, and each plate is oriented in substantially the same general circumferential direction to divert separate streams of liquid complex from the outer annular launder into the inner annular launder and to impart a circulatory flow of the liquid complex in the inner launder, so that the circulating liquid complex may be discharged from the inner launder tangentially into the frusto-conical tube.

16. Apparatus according to claim 11, in which the annular launder constitutes an inner launder immediately adjacent the periphery of the top portion of the frustoconical tube, an outer annular launder surrounding the inner annular launder, the associated devices include a barometric inlet tube connecting a source of liquid complex with the interior of the outer launder for feeding liquid complex therethrough, a plurality of circumferentially spaced passageways connect the outer launder with the inner launder for the passage of liquid complex the rethrough, the inner and outer walls of the outer annular launder extend substantially higher than the top of the frusto-conical tube so that the outer launder may contain an annular body of the liquid complex with a liquid level substantially higher than the normal liquid level in the inner annular launder to establish a hydrostatic head in the outer annular launder for impelling liquid complex under accelerated velocity through the fit passageways from the outer annular launder to the inner annular launder.

17. Apparatus according to claim 16, in which the passageways connect with inlet tubes extending at an acute angle from the outer exterior wall of the inner annular launder part Way into the interior of the outer annular launder, the inlet end of said inlet tubes opens into the outer launder and the outlet end of the inlet tubes opens tangentially into the inner launder, and each inlet tube is oriented in substantially the same general circumferential direction to accelerate circulation of the liquid complex in its normal direction of How in the inner launder.

18. Apparatus according to claim 16, in which the associated devices also include a plurality of upright deflecting vanes integrally secured to the top over-flow lip of the frusto-conical tube at an acute angle, a free end of each vane extends from the over-flow lip over the frusto-conical tube, and each deflecting vane is oriented in substantially the same general circumferential direction for discharging liquid complex tangentially into the frusto-conical tube and onto its inner distributing surface.

References Cited by the Examiner UNITED STATES PATENTS 1,688,426 10/ 1928 Lannon 88 2,032,215 2/1936 Kemmer 7588 2,424,640 7/ 1947 Spooner 22-57.2 2,720,456 10/ 1955 Davey 7588 2,823,111 2/ 1958 Davey 7588 3,031,296 4/1962 Davey 77-88 BENJAMIN HENKIN, Primary Examiner.

DAVID L. RECK, Examiner. 

1. IN THE METHOD OF SEPARATING AND RECOVERING A RELATIVELY VOLATILE CONSTITUENT FROM A LIQUID COMPLEX CONTAINING THE SAME IN ASSOCIATION WITH A LESS VOLATILE CONSTITUENT, THE LIQUID COMPLEX BEING UNDER VACUUM IN AN ENCLOSED SPACE WHILE IT DECENDS BY GRAVITY CONTINUOUSLY AS A FILM SUPPORTED BY THE INNER SURFACE OF AN INVERTED GENERALLY CIRCULAR HOLLOW FRUSTO-CONICAL EVAPORATING ZONE WITHIN THE ENCLOSED SPACE, THE LARGER END OF THE CIRCULAR FRUSTOCONICAL EVAPORATING ZONE BEING UPPERMOST AND THE SMALLER END OF THE CIRCULAR FRUSTO-CONICAL EVAPORATING ZONE BEING LOWERMOST, MAINTAINING WITHIN THE FRUSTOCONICAL ZONE, AND SUBSTANTIALLY IN LATERAL OPPOSITION TO THE EVAPORATING ZONE, A SUBSTANTIALLY CONCENTRIC UPRIGHT CIRCULAR CONDENSING ZONE FOR THE MORE VOLATILE CONSTITUENT, MAINTAINING THE ENCLOSED SPACE UNDER SUFFICIENT VACUUM TO EVAPORATE PROGRESSIVELY THE MORE VOLATILE CONSTITUENT FROM THE SUPPORTED THIN FILM OF LIQUID COMPLEX, CONDENSING THE RESULTING VAPOURS OF THE MORE VOLATILE CONSTITUENT IN THE UPRIGHT CONDENSING ZONE FIRST AS A SOLID CAKE AND LATER AS A LIQUID, PROGRESSIVELY WITHDRAWING FROM THE ENCLOSED SPACE THE CONDENSED LIQUID OF THE MORE VOLATILE CONSTITUENT, AND PROGRESSIVELY WITHDRAWING FROM THE ENCLOSED SPACE THE LESS VOLATILE CONSTITUENT WHILE STILL IN LIQUID FORM, THE IMPROVEMENT WHICH COMPRISES THE COMBINATION THEREWITH OF THE STEPS OF (A) FLOWING THE LIQUID COMPLEX UNDER PRESSURE ONTO THE INNER AND UPPER PART OF THE HOLLOW INVERTED FRUSTOCONICAL EVAPORATING ZONE AT A CAREFULLY CONTROLLED ANGULAR VELOCITY; (B) IMPARTING A TRANSVERSE TANGENTIAL CIRCUMFERENTIAL FLOW OF THE LIQUID COMPLEX AROUND AND IN SWEEPING CONTACT WITH THE INNER SUPPORTING DISTRIBUTING SURFACE OF THE INVERTED FRUSTO-CONICAL EVAPORATING ZONE; (C) SPREADING THE FLOWING LIQUID COMPLEX SUBSTANTIALLY EVENLY OVER THE UPPER PART OF THE INNER SUPPORTING DISTRIBUTING SURFACE OF THE INVERTED FRUSTO-CONICAL EVAPORATING ZONE TO FORM THEREON A THIN EVEN FILM OF THE LIQUID COMPLEX; (D) MAINTAINING THE TRANSVERSE TANGENTIAL FLOW OF THE THIN EVEN FILM OF LIQUID COMPLEX IN HUGGING CONTACT WITH THE INNER SURFACE OF THE INVERTED FRUSTO-CONICAL EVAPORATING ZONE AS THE FILM OF LIQUID DECENDS IN THE EVAPORATING ZONE; (E) CONTINUING THE RESULTING SWIRLING SPIRAL FLOW OF THE THIN EVEN FILM OF LIQUID COMPLEX ON THE SUPPORTING SURFACE OF THE EVAPORATING ZONE WHILE VAPOURIZING THE MORE VOLATILE CONSTITUENT THEREFROM AND CONDENSING THE RESULTING VAPOURS ON THE COOLER AND CONDENSED SOLID CAKE OF MORE VOLATILE CONSTITUENT; (F) ALLOWING THE EVEN THIN FILM OF LIQUID TO DECEND TO THE BOTTOM OF THE INVERTED HOLLOW FRUSTO-CONICAL EVAPORATING ZONE AND OF THE ENCLOSED SPACE WITHOUT SPLASHING TO AVOID CONTAMINATION OF THE VAPOUR FROM, AND CONDENSED SOLID CAKE OF, THE MORE VOLATILE CONSTITUENT WITH DROPLETS OF LIQUID CONTAINING THE LESS VOLATILE CONSTITUENTS; (G) PASSING THE THIN EVEN FILM OF LIQUID FROM TOP TO BOTTOM OF THE EVAPORATING ZONE WITHOUT SUBSTANTIAL VOLATILLIZATION OF THE LESS VOLATILE CONSTITUENT OF THE LIQUID; AND (H) REMOVING SEPARATELY THE RESULTING LIQUIDS FROM THE BOTTOM OF THE INVERTED HOLLOW FRUSTO-CONICAL EVAPORATING ZONE AND OF THE ENCLOSED SPACE. THUS EFFECTING A RELATIVELY SHARP SEPARATION AND RECOVERY OF THE MORE VOLATILE CONSTITUENT FROM THE LESS VOLATILE CONSTITUENT OF THE ORIGINAL LIQUID COMPLEX. 